Sale of Future Royalties - Liability Activity (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Liability Related To Sale Of Future Royalties [Roll Forward]
Net liability related to sale of future royalties - beginning balance	$ 18,992
Non-cash royalty revenue	(656)
Non-cash interest expense	1,039
Net liability related to sale of future royalties - ending balance	$ 19,375